Oracle sql 在插入/更新时触发以计算 2 个值并更新第三个值

Question

我想创建一个触发器，通过计算 2 个值来更新行并更新第三个值：

CREATE TABLE Customers (
    Cust_ID INTEGER PRIMARY KEY,
    Dates TIMESTAMP WITH LOCAL TIME ZONE,
    Quantity dec(7,2) NOT NULL,
    Price_per_item dec(7,2) NOT NULL,
    Total_price dec(7,2)
);

我已经这样做了：

CREATE OR REPLACE TRIGGER cust_after_insert AFTER INSERT 
ON Customers
FOR EACH ROW
BEGIN
    UPDATE Customers
    SET 
    DATES = CURRENT_TIMESTAMP,
    Total_price = Quantity * Price_per_item;
END;

我尝试同时查看和编辑表格时遇到某种错误。

我也试过这个：

CREATE SEQUENCE cust_Seq START WITH 1 INCREMENT BY 1;
CREATE OR REPLACE TRIGGER cust_trig BEFORE INSERT ON Customers
FOR EACH ROW
BEGIN
  SELECT cust_Seq.nextval INTO :new.Fuel_ID FROM dual;
  SELECT CURRENT_TIMESTAMP INTO :new.DATES FROM dual;
  SELECT Quantity * Price_per_item INTO :new.Total_price FROM dual;
END;
/

我更喜欢第二个选项，如果更新也会发生，我将需要一些东西。

Answer 1

第二种方法的方向是正确的，但它需要一些调整来处理Total_price 的计算以及处理updates：

CREATE SEQUENCE cust_Seq START WITH 1 INCREMENT BY 1;
CREATE OR REPLACE TRIGGER cust_trig BEFORE INSERT OR UPDATE ON Customers
FOR EACH ROW
BEGIN
  IF INSERTING THEN
    SELECT cust_Seq.nextval INTO :new.Fuel_ID FROM dual;
    SELECT CURRENT_TIMESTAMP INTO :new.DATES FROM dual;
  END IF;
  :new.Total_price :=  :new.Quantity * :new.Price_per_item;
END;
/